Recovery of fibers from a fiber processing waste sludge

ABSTRACT

A process of recovering a useful population of fibers and fines from the waste stream of fiber processing facility is disclosed. Steam explosion of the fiber-containing waste stream is used to increase the separation efficiency of the fibers from the ash. The steam explosion also enhances the quality of the recovered fibers and fines, providing a population of recovered fibers which can be incorporated into the fiber component of a tissue or absorbent paper product.

FIELD OF THE INVENTION

[0001] This invention relates to a process for recovering a useablepopulation of fibers and fines from the waste sludge of a fiberproduction or fiber handling facility.

[0002] In particular, this invention provides a steam explosion processand a resulting product which permits the separation of a usefulpopulation of fibers and fines from the waste streams of fiberproduction processes such as a waste paper recovery operation or fromthe waste stream of a papermaking process. The process is useful infiber and fine recovery from white water waste streams from paper makingoperations and waste sludge from the de-inking and processing of wastepaper. The present invention not only increases the amount of usablefibers and fines recoverable from the waste stream, but increases thefiber quality of the recovered fibers. Additional benefits include aconcomitant reduction in the solid volume of the waste stream andincreases the usable fiber content available from the initial rawmaterial. The process steps of the present invention yield a fiber ofimproved quality suitable for making tissue products such as toilet andfacial tissues, paper towels, and napkins.

DESCRIPTION OF THE PRIOR ART

[0003] Waste sludge from fiber production and papermaking facilitiestypically contain numerous fibers and fines. In particular, efforts torecover the fibers and fines from the waste sludge streams of paperfiber recovery plants have been limited, in part, by the high ashcontent of the sludge. Conventional fiber screening techniques alsoretain the ash particulates. The high ash content renders the recoveredfibers and fines undesirable for quality end products.

[0004] Paper is conventionally made by draining a low consistencydispersion of cellulose fiber pulp, fillers, and additives through apaper machine “wire” (essentially an endless mesh or sieve). A certainamount of solid material passes through the wire with the suspendingwater and is, thus, not retained in the wet paper web formed on thewire. The drained liquid suspension, known generally in the industry as“white water,” carries entrained solid material. White water from whichthe suspended particles have been removed is reused in the papermakingprocess to the extent possible.

[0005] Obviously, wastepaper, if it can be recycled, is a much cheaperand environmentally friendly source of wood pulp for making paper.Before wastepaper can be reused as recycle material, however, thewastepaper must be de-inked. De-inking processes remove inks and coatingmaterials from the wood fibers. Thus, when recycled fibers, as opposedto virgin pulps, are used in the papermaking process, the drained liquidsuspension will contain additional types of waste materials such as inksand hot melt adhesives.

[0006] Unused white water and de-inking effluents must be treated beforebeing discharged from the paper mill. Treatment normally involvespassing the effluent through a clarifier, prior to which flocculants areadded to promote sedimentation of solid material suspended in the water.A biological treatment with microorganisms is also commonly performed toreduce the biological oxygen demand (BOD) of the liquid effluent beforeit is discharged. As can be expected, disposal of the unused white waterand de-inked effluents results in costs to the papermaking facility.

[0007] The sediment accumulated in the clarifier is a sludge composed ofpulp fibers, fiber particles or fines, fillers, pigments, and othermiscellaneous debris such as grit, sand, plastic particles, generaldirt. Many of the sludge components are fillers, pigments and the likethat were added to the pulp during the sheet-forming process for thepurpose of producing desired properties in the finished paper. Suchproperties include proper surface, opacity, strength and brightness. Forexample, finely ground inorganic fillers, such as talc, certain clays,calcium carbonate, blanc fixe, and titanium dioxide may be added topapers to improve surface smoothness, whiteness, printability andopacity. Sizing agents, such as soaps, gelatins, and rosins (with alum),wax emulsions and starches, may be added to papers for improvingresistance to penetration by liquids. In addition, coloring agents, suchas acid, basic, direct and sulfur dyes and

[0008] natural and synthetic pigments may be added for coloringpurposes. Any of such products may ultimately end up in the clarifier aspart of the sludge. In addition, because the clarifier is usually alarge open air tank, other debris such as leaves, branches, insects,etc. can also become part of paper sludge. The major constituents of thesludge, however, are generally fiber/fines and the inorganic fillerscalcium carbonate and clay.

[0009] Most de-inking processes involve the use of flotation andwashing. In de-inking processes, wastepaper is first washed and thenpulped with dilute sodium hydroxide or surfactants in a pulper tank tocause the fibers to swell and loosen the ink and coating materialparticles contained thereon. (These coating materials include thepreviously mentioned clays, talc, etc.) After pulping, the pulp stocksgo through screening, cleaning, washing, floatation, and bleaching tofurther remove trash, stickies, inks, ash, and short fiber fines. Duringthe washing and floatation stages, most ash, stickies, and short fiberfines are separated from the pulp stock. Thus, when the sludge comesfrom a mill using recycled waste paper, this sludge may also haveaccumulations of adhesives (otherwise known as “stickies”), foreignbodies (such as pieces of plastic material or metal, otherwise known as“contraries”) in very small quantities, and other additives, such asthose described above, that are used in the papermaking process.

[0010] Normally, the sludge is drawn off from the clarifier at about 2.5percent consistency (or “percent dry solids content”) and is thendewatered to a consistency of around 20 to 55 percent, for example, bymeans of rotary vacuum filters, screw presses, or belt presses.Dewatering reduces the weight of material going to the landfill andreduces the charges for landfill disposal because these are typicallybased on weight. Since the majority of the weight in the sludge comesfrom water, it behooves the sludge processor to remove as much water aspossible. The dewatered sludge is in a semi-solid state and usuallycontains about 40 percent to about 80 percent by dry weight relativelyfine wood fibers and from about 20 percent to about 60 percentinorganics (also referred to as “ash”) and the additives mentionedabove. The material typically is a crumbly, not very cohesive materialthat appears to be dry. At thirty percent consistency, most sludges aremore like dry solids as opposed to a suspension or dispersion. Becauseof the non-cohesive character of sludge, the materials handlingequipment for moving, storing and transporting are generally the same asfor dry materials. Once in this state, the sludge is then capable ofbeing collected and transported for disposal in landfills.

[0011] According to some sources, it is estimated that the amount of drywaste (waste sludge with substantially all of the residual waterremoved) produced due to paper processing exceeds 4.6 million tons peryear. This sludge is produced by both papermaking from virgin pulp andpapermaking from recycled fibers. A typical de-inking plant employingrecycled fibers processes about 100 dry tons of waste paper into about65 to about 80 dry tons of recycled (reusable) fiber. The remaining 20to 35 tons of waste paper is unusable, and becomes part of the sludgeproduced by the deinking plant. After recycled fiber sludge is dewateredwith various suitable dewatering devices, including, for example, a beltpress or screw press, 100 dry tons of waste paper still produce fromabout 70 to about 120 wet tons of sludge which must be disposed.

[0012] Moreover, the sludge produced during the making of tissue from anintegrated mill with a recycled fiber plant produces 10 times the amountof sludge produced during the making of tissue from virgin pulp. Thetypical virgin pulp tissue making process with a 200 ton capacityproduces 10 tons of sludge per day while the typical tissue making withrecycled fiber plant produces 100 tons of sludge per day.

[0013] Conventional methods for disposing of sludges include landfill,land spreading, composting and incineration. Landfill and land spreadingsites are being depleted at an alarming rate, and the establishment ofnew sites is difficult due to environmental concerns. In addition, thecost associated with using landfills to dispose of sludge is constantlyincreasing. For example, paper manufacturers typically spend about$30/wet ton to send sludge to the landfill. Composting and incinerationof sludge also raise environmental concerns. Some innovative sludgedisposal techniques include processing the sludge into pellets for fuelor into lightweight aggregates for construction, pyrolysis,gasification, and incorporation into cements. However, these techniquesgenerally require the use of complex methods and expensive equipment. Inaddition, attempts to recycle sludge to make paper have beenunsuccessful because the process is inefficient due to drainage problemsresulting from the presence of slow drying fines which tend to clog thewires and other equipment.

[0014] Due to the extremely large amounts of waste sludge generated fromboth the virgin pulp papermaking and the recycled fiber papermakingprocesses, new uses of sludge are needed in order to curtail thedisposal problems presently being encountered. Some attempts have beenmade to create such uses.

[0015] The prior art sets forth basically five different approaches forutilizing sludge in useful products:

[0016] (1) Pelletizing the sludge using high pressure and binders wherethe sludge is dried before pelletizing. The pellets can be used asabsorbents or chemical carriers, e.g., fertilizer. Alternatively, largediameter pellets or cylinders are used as fuel.

[0017] (2) Extracting the fibers or fillers from sludge in various waysto subsequently use the extracted material in a paper and/or ceramicproduct. These are both wet and dry processes.

[0018] (3) Mixing the sludge with other construction ingredients such asconcrete or plastic to embody the sludge as reinforcing fibers orfiller. Again these are both wet and dry processes.

[0019] (4) Direct molding of sludge into large shapes (i.e., large crosssection) and drying. These products are construction blocks or boardsand can be made using both wet and dry processes. Some of these can befired to burn out the cellulosic and polymeric materials, leaving aceramic product.

[0020] (5) Some sludges are formed into particulates or briquettes ofvarious forms and sizes. These are subsequently carbonized to make anactivated carbon product.

[0021] U.S. Pat. No. 4,303,019 to Haataja discloses the making ofpellets by molding paper mill sludge blended with a fibrous reinforcingmaterial. U.S. Pat. No. 5,215,625 to Burton discloses the making ofproducts such as stepping stones, acoustic paneling, flower pots andplanters, sculptures, shipping containers and packing materials, and thelike, from waste products such as ink and waste slurry from pulpmanufacturing. The incorporation of de-inking byproducts from wastepaperrecycling operations and pulp mill clarifier sludge into drywall andother gypsum-based building products is disclosed in U.S. Pat. No.5,496,441 to Tran.

[0022] Attempts have also been made to recover and re-use the rawmaterials from paper mill waste sludge. For example, U.S. Pat. No.5,478,441 to Hamilton, discloses a process for recovering such rawmaterials. U.S. Pat. No. 5,332,474 to Maxham discloses a process forproducing a papermaking filler product from the fiber fines/clayfraction of a pulp, paper, paperboard, or deinking mill waste solids.

[0023] While considerable prior art exists with regard to methods forhandling, utilizing or recycling of sludge as outlined above, in actualfact there has been little commercial implementation. The majority ofthe materials classified as sludge from both deinking operations as wellas conventional pulp and paper mills ends up in landfills or isdiscarded or disposed of in some other way. The major reason is that fewof the many procedures available to convert sludges can produce productsthat have significant value.

[0024] The need to develop methods and processes that would use thesewaste materials, however, is growing. It is likely that environmentaland regulatory pressures to recycle paper and paper products willincrease. This will mean there will be more de-inking and recyclingoperations in the future. In addition, it is likely that the percentageof inorganic materials in recycled paper, such as calcium carbonate andclay, will increase for a number of reasons. For example, calciumcarbonate improves the long term stability of printing papers becausethe alkalinity of the calcium carbonate reduces the rate ofdiscoloration and embrittlement of the paper. Additionally, both calciumcarbonate and clay are used to increase the opacity of paper. Inprinting items such as magazines or advertising supplements, addition ofinorganic materials allows for reductions in the amount of fiber usedfor the paper. The purpose for the added inorganic material is toprovide superior opacity. In addition to the improved opacity,incorporation of clay as a coating or filler and calcium carbonate as afiller also provide improvements to the surface of the paper such thatthe quality of the printing is improved. Furthermore, wood pulp, eventhough it is a renewable resource, is becoming more expensive. The costof wood pulp currently exceed the cost of calcium carbonate or clay, andit, therefore, makes economic sense to include considerable amounts ofthese fillers in paper.

[0025] Steam explosion has been used to defiber paper material asdescribed in U.S. Pat. No. 5,262,003 to Chupka et al. and in U.S. Pat.No. 4,312,701, which are both incorporated herein by reference. Asfurther discussed in Chupka, non-fibrous contaminants subjected to thesteam explosions have a reduced particle size and are more readilywashed out of the fiber suspensions.

[0026] Steam explosion is also used in the defibration of wood chips astaught in U.S. Pat. No. 4,798,651 to Kokta, incorporated herein byreference. In Kokta, wood chips are chemically treated followed bysteaming and explosive decompression to defibrate the chips.

[0027] In U.S. Pat. No. 4,163,687 to Mamers et al., a nozzle design isdisclosed which is used in cellulosic defibration which increases usablefiber content from wood chips and results in less fiber damage.

[0028] In U.S. Pat. No. 5,262,004 to Gilbert, incorporated herein byreference, steam explosion is used as part of a chemical separation andrecovering process of chemical preservatives from wood chips frompreviously treated wood.

[0029] U.S. Pat. No. 5,122,228 to Bouchette et al., incorporated hereinby reference, discloses a steam explosion process which is used in thede-inking of waste paper. The temperature ranges used by Bouchette arereported to decrease particle size of contaminants and increase theability to strip contaminants from the fibers.

[0030] Australian Patent Office Application AU-B-29615/92, correspondingto U.S. application Ser. No. 840,370 filed Feb. 24, 1992, discloses asteam explosion of mixed grades of high and low quality waste paperwhich have been delignified by alkaline digestion.

[0031] As will be seen from the description and illustrations to follow,none of the above-identified references discloses or anticipates thepresent invention directed to the process of treating waste sludge andwaste liquor with steam explosion to increase the recoverable yield offibers and fines from the waste stream. Further, none of the referencesteach or suggest that the useful fiber characteristics of an individualfiber can be improved for absorbent products by the steam explosionprocess.

SUMMARY OF THE INVENTION

[0032] The present invention recognizes and addresses some of thelimitations of prior art fiber production in papermaking processes whichdiscard a large percentage of fibers and fines as an unsalvageableand/or non-useful waste material.

[0033] It is, therefore, a general object of the present invention toprovide a process for recovering a useful opulation of fibers and finesfrom the waste stream of a fiber production, waste paper recycling, orpapermaking process. In carrying out the present process, it has beenfound that a steam explosion process may alter the morphology of fibersand fines contained within a waste stream, the altered morphologyfacilitating not only the separation of the fines from the waste stream,but improving their useful qualities in a paper product or papermakingprocess.

[0034] The invention sets forth a process by which a supply of treated,recovered fibers and fines have superior fiber quality characteristicsfor absorbent products than similar untreated fibers and fines. Thepresent invention enables both the volume and dry solid content of wastestreams to be reduced by the recovery of additional fibers and finesfrom the waste stream. As a result, it is possible to increase thepercentage of fibers and fines from the starting material. It is furtherpossible to incorporate the increased percentage of fibers and finesinto a finished paper product without lowering the quality of thefinished product.

[0035] These and other useful objects of this invention are achieved bya process and resulting product which provides a waste sludge streamcontaining uncaptured fibers and fines from a fiber processing facility;subjecting the waste stream to an elevated temperature and pressure;explosively releasing the pressure from said waste stream; passing thenow treated waste material through a filter recovery apparatus; and,separating a population of recovered fibers and a population ofrecovered fines from the waste stream.

[0036] Another aspect of the present invention concerns an absorbentstructure comprising modified cellulosic fibers prepared by the processdisclosed herein.

[0037] One embodiment of such an absorbent structure is a handsheetcomprising the modified cellulosic fibers prepared by the processdisclosed herein, wherein the handsheet is prepared by a wet laidprocess.

BRIEF DESCRIPTION OF THE DRAWINGS

[0038]FIG. 1 is a graphical depiction of data comparing the screeningefficiency of varying quantities of untreated waste sludge.

[0039]FIG. 2 is a graphical depiction of data comparing the screeningefficiency with respect to ash content of varying amounts of untreatedwaste sludge.

[0040]FIG. 3 is a graphical depiction of data comparing the screeningefficiency of fibers and fines from waste sludge following treatment ofthe sludge by steam explosion.

[0041]FIG. 4 is a graphical depiction of data setting forth the treatedwaste sludge retained ash content.

[0042]FIG. 5 is a graphical depiction of data comparing the CanadianStandard Freeness values of handsheets with varying levels of recoveredfibers from treated sludge.

[0043]FIG. 6 is a graphical depiction of data comparing the burst indexof handsheets prepared with varying levels of incorporated treatedfibers.

[0044]FIG. 7 is a graphical depiction of data comparing the tensileindex for handsheets formed with varying levels of treated fibers.

[0045]FIG. 8 is a graphical depiction of data comparing the tensilestretch for handsheets formed with varying levels of treated fibers.

[0046]FIG. 9 is a graphical depiction of data comparing the tear indexfor handsheets formed with varying levels of treated fibers.

[0047]FIG. 10 is a graphical depiction of data comparing the effect onopacity of various fiber levels incorporated into handsheets.

Detailed Description of A Preferred Embodiment

[0048] It is to be understood by one of ordinary skill in the art thatthe present discussion is a description of exemplary embodiments only,and is not intended as limiting the broader aspects of the presentinvention, which broader aspects are embodied in the exemplaryconstruction.

[0049] The present invention addresses some of the objects and needsdiscussed above by providing a process using steam explosion to treatvarious fiber and fine containing waste streams. As used herein, “wastestream” refers to the waste stream from a waste paper recyclingoperation or the liquid waste stream (white water) from a papermanufacturing process, all of which may contain varying levels of fibersand fines within the waste.

[0050] The term “fiber” refers to natural fibers derived from vegetablematter and that has a length usually many times greater than its width,and that typically possesses tensile strength, pliability, andresistance to mechanical abrasion. This term may also encompassessimilarly shaped man-made objects which may be present in waste paperproducts.

[0051] The term “fines” refers to short, naturally occurring fibers aswell as fragments of fibers. Depending upon the underlying fiber processinvolved, the term “fines” may refer to different lengths of fibers. Asbroadly defined here, “fines” refers to the population of fibers withina fiber processing stream having an average length as determined byeither a length average calculation or a weight average calculation,which falls outside a desired, useful range. Within a virginpaper-making operation which prefers longer, intact fibers, the averagelength of the fines may be greater than the fine population of a wastepaper recycling facility.

[0052] No matter how defined, the population of fines heretoforeconsidered as unsalvageable waste or of inferior quality can now berecovered. In doing so, the recovery process enhances the fiber-likequalities of the fines by increasing the curl value, increasing thefiber diameter along a portion of the fiber, and by increasing thewicking properties of the recovered, treated fines.

[0053] By way of example, the Kajaani FS-200 average fiber lengthpresent within the sludge utilized by the examples herein, fall withinthe range of 0.60 to 0.85 mm and which corresponds to a Kajaani FS-200length weight average of between 1.75-2.00 mm. Accordingly, the averagefiber length present within the waste sludge material is considered a“fine” for the purposes of this invention. Further, the fiber materialwhich is shorter than the average range is also considered a fine. Whilethe fiber material which has a length equal to or less than the averagefiber length is considered a fine, it is recognized that longer fibersare also present in the waste stream. Such longer fibers are alsorecoverable and constitute a valuable recovered fiber product and whichalso has improved absorptive fiber properties. It is the longerpopulation of fibers which are believed to be separated and retained onthe Bauer-McNett classifier screen of 200 mesh or larger.

[0054] Heretofore, significant amounts of fibers and fines have beenconsidered a waste product in tissue and paper production. The fibersand fines have historically proven difficult to isolate and contain ahigh degree of contaminants such as ash.

[0055] The ash content of recycled fiber sludge is indicative of theamount of additives which are incorporated in the waste paper. The ashcontent of the recycled sludge is generally about 20 to about 80%. Wastepaper containing high filler and coating materials, for example,magazines, provides a recycled sludge having a high ash content. By wayof comparison, newsprint de-inking mills generally produce a lower ashcontent waste sludge.

[0056] The ash content of the recycled fiber sludge employed in themethods of the present invention can vary and depends, for example, uponthe source mill, the particular components of the recycled sourcematerial, and the like. However, it is believed that the beneficialeffects of the present invention on the ash content, renders theinvention suitable with all varying levels of ash content. Further, tothe extent the present invention improves the physical properties of thefibers within the waste stream, such improvements occur irrespective ofthe ash content. Accordingly, a fiber-containing waste stream having anegligible ash content would provide a useful source of fibers for steamtreatment.

[0057] In particular, fines have been considered a waste product in thetissue and paper production industry since fines typically retard waterdrainage, confer low air permeability to the formed webs or sheets,exhibit a higher degree of chemical reactivity which results in greaterchemical cost, and tend to promote greater fiber-fiber bonding which,while increasing product strength, imparts an often undesired stiffnessto the paper product. In particular, the fiber component from paperrecycling waste sludge has heretofore been considered unsalvageable inthat the reclaimed fibers have had an unacceptably high ash content.

[0058] In accordance with one aspect of the present invention is thediscovery that the steam explosion of the waste sludge alters the fineshape. As set forth in co-inventor Sheng-Hsin Hu U.S. patent applicationSer. No. 08/767,607 filed on Dec. 17, 1996 entitled “Treatment Processfor Cellulosic Fibers” and incorporated herein by reference, steamexplosion can be used to increase the curl value of individual fibers.Further, the steam explosion has been found to increase the wickingproperties of the resulting product incorporating the steam explodedfibers, and increases the separation efficiency of the fibers and finesfrom the waste sludge. The steam explosion permits the separation offibers and fines from the waste sludge and does so in a manner whichprovides a population of recovered fibers having a low ash content. Thisrecovered population of fibers has demonstrated improved burst index,tear index, tensile index, and tensile strength compared to handsheetsincorporating a similar percentage of untreated sludge fibers.

[0059] It is understood and appreciated by those having ordinary skillin the art that the cellulosic fibers in the waste streams describedherein will be substantially in the form of individual cellulosic fibersalthough some individual fibers may be in an aggregate form. The currentprocess, then, is in contrast to known steam explosion processes thatgenerally treat cellulosic fibers that are typically in the form ofvirgin wood chips or the like.

[0060] It is believed that the present steam treatment of the sludge andsludge fibers brings about changes to the fiber and fine propertieswhich correspond closely with the results reported in the co-pendingapplication referenced above.

[0061] It is believed that any combination of high pressure, hightemperature, and time which is effective in achieving a desired degreeof fiber modification is suitable for use in the present invention.Further, such combination of pressure, temperature and time are believedto have beneficial effects on the ash content of the sludge, therebyoffering an improved quality of fiber while increasing the efficiency offiber separation from the sludge.

[0062] As a general rule, it is believed that the cellulosic fibers inthe waste material may be beneficially treated at a temperature in therange from about 130° C. to about 250° C., suitably from about 150° C.to about 225° C., more suitably from about 160° C. to about 225° C., andmost suitably from about 160° C. to about 200° C.

[0063] The elevated temperature and pressures are applied over a timeperiod within a range from about 0.1 minutes to about 30 minutes,beneficially from about 0.5 minutes to about 20 minutes, and suitablyfrom about 1 minute to about 10 minutes. In general, the higher thetemperature employed, the shorter the period of time generally necessaryto achieve a desired degree of modification of the cellulosic fibers,fines, and ash present in the waste stream. As such, it may be possibleto achieve essentially equivalent amounts of modification for differentfiber-containing waste streams by using different combinations of hightemperatures and times.

[0064] As a general rule, it is believed that the cellulosic fibers inthe waste stream would be treated at a pressure that issuper-atmospheric and within the range of about 40 to about 405 poundsper square inch, suitably from about 40 to about 230 pounds per squareinch, and more suitably from about 90 to about 230 pounds per squareinch.

[0065] Without intending to be bound by theory, it is believed that thesteam explosion process causes the cellulosic fibers to undergo aphysical modification. The physical modification includes a curlingphenomenon which helps in the physical separation of the fibers as wellas alters other properties such as liquid absorption or liquid handlingcapabilities.

[0066] The curl of a fiber may be quantified by a curl value whichmeasures the fractional shortening of a fiber due to kink, twist, and/orbends in the fiber. As used in the present invention, a fiber's curlvalue is measured in terms of a two-dimensional plane, determined byviewing the fiber in a two-dimensional plane. To determine the curlvalue of fiber, the projected length of a fiber as the longest dimensionof a two-dimensional rectangle encompassing the fiber (I) and the actuallength of the fiber (L) are both measured. An image analysis method maythen be used to measure L and I. A suitable analysis method is describedin U.S. Pat. No. 4,898,642 incorporated herein in its entirety byreference. The curl value of a fiber can then be calculated from thefollowing equation:

Curl value=(L\I)−1

[0067] It has been found in accordance with this invention that thecellulosic fibers following steam treatment are suitable for use in awide variety of applications. One useful aspect of the recovered fibersand fines are that they may be reintroduced into the respective processstream associated with the initial waste stream used to isolate thefibers. It is believed that the recovered fibers and fines are suitedfor use in disposable absorbent products such as diapers, adultincontinent products, bedpans, sanitary napkins, tampons, and otherabsorbent products including wipes, bibs, wound dressings, surgicalcapes, and tissue-based products including facial or bathroom tissues,household towels, wipes, and related products. Accordingly, the presentinvention relates to a disposable absorbent product comprising thecellulosic fibers treated according to the process of the presentinvention. Further, in another aspect, the present invention relates toany paper product comprising the recovered and treated cellulosic fiberand fines treated in accordance with the present invention.

Test Procedures

[0068] Sludge Treatment

[0069] Approximately 100 grams of waste sludge at 45 percent consistencywas obtained from a waste paper fiber recycling facility atKimberly-Clark Corporation, Owensboro facility. The waste sludge wasplaced into a two-liter reactor vessel (Stake Technologies Ltd.) wherehigh pressure steam was injected into the reactor thereby achieving atemperature of 202° C. and a pressure of 200 psi. The sludge wasretained for time intervals of 2 minutes and 5 minutes. Following theappropriate retention time, a blow valve was opened and the sludge wasblown into a collection tank maintained at ambient conditions. Thecollection tank was suitably vented so that transient pressureaccumulations within the collection tank during the sludge dischargewere minimized so as to achieve a rapid pressure drop of the sludgeduring the discharge step. Three repetitive runs were conducted for eachretention time and the respective samples were combined for furtheranalysis.

[0070] Fiber Collection

[0071] The two-minute and five-minute treated sludge samples along withcontrol (untreated sludge) samples were subsequently dispersed in aBritish Disintegrator (Testing Machines, Inc.) for three minutes, andthen evaluated with a Bauer-McNett classifier (Testing Machines, Inc.)for 20 minutes. The classifier comprises six ten-liter cells separatedby 14, 28, 48, 100, and 200-mesh screens. All cells were filled withwater and subjected to constant agitation. 10 and 20-gram samples ofoven dry weight of the treated and control sludge were placed intorespective first cells and passed through each screen in sequentialorder from the lowest to the highest mesh screen.

[0072] After 20 minutes, the water was drained from each cell and theclassified sludge samples were collected, weighed, and evaluated for ashcontent using standard methods as established in TAPPI Test MethodT-211-OM-93.

[0073] The collected samples which were retained by the 200-mesh screensor larger were combined and incorporated into wet-laid handsheets. Theremaining material smaller than the 200-mesh screen was comprisedlargely of fines. While this population of fines was not used in thepresent examples, it is believed that these fines also show improvementsin fiber quality similar to the results reported below.

[0074] Preparation of Wet-Laid Handsheet

[0075] A standard 7½ inch by 7½ inch handsheet was prepared using thedesired fiber samples by using a 8 inch by 8 inch cast bronze wet-laidhandsheet former mold, available from Voith Corporation. The handsheetshad a basis weight of about 60 grams per square meter.

[0076] The handsheets were made using ratios of 30, 70 and 100 percentsteam exploded recovered fibers mixed, when applicable, with theappropriate percentages of recycled fiber wet lap obtained from theKimberly-Clark Owensboro facility. The recycled fiber wet lap is therecovered product, the production of which provided the original wastesludge which was used in the steam explosion treatment process.

[0077] A British Disintegrator mixer, available from Testing Machines,Inc, was filled with about 2 liters of distilled water at roomtemperature (23° C.) and about 45.0 grams of the fiber sample. Thecounter on the British Disintegrator was set to zero and was turned onuntil the counter ran to about 600. The contents of the BritishDisintegrator were then poured into a vessel filled with about 8 litersof distilled water.

[0078] The handsheet former, having an approximate 12 inch deep chamber,was filled with tap water to about 5 inches below the top of thehandsheet former chamber. The contents of the bucket were then pouredinto the handsheet former chamber where a dedicated stirrer was thenused to mix the suspension in the handsheet former chamber. The stirrerwas moved slowly up and down 6 times to cause small vortexes, but toavoid causing large vortexes, in the square pattern of the handsheetformer. The stirrer was then removed and the suspension was drainedthrough the forming screen of the handsheet former. The handsheet formerwas then opened and two layers of blotting paper were placed on top ofthe handsheet. A roller, applying the equivalent of about 308kiloPascals of pressure inch, was moved back and forth one along eachside and the center of the formed handsheet. The blotting paper, withthe formed handsheet attached, was then lifted off the forming screen.The blotting paper was then placed on a table such that the formedhandsheet faced upwards. An 18 inch, 4 mesh, stainless steel screen wasplaced on top of the handsheet. The blotting paper, handsheet, andscreen were then flipped so that the screen was on the bottom and theblotting paper was on top. The blotting paper was then peeled off of thehandsheet, leaving the handsheet on the screen. The handsheet istransferred, wire side up, to the polished convex surface of an 8 inchby 8 inch dryer hot plate. A canvas cover is placed over the convexsurface and handsheet and is weighted down to prevent drying inducedwrinkling. The handsheet is dried for 2 minutes and then removed forsubsequent evaluation.

[0079] Recovered Fiber Properties

[0080] Set forth in Table 1, and as further discussed in reference tothe Figures, are various fiber properties as further discussed inreference to the accompanying figures. As seen in FIG. 1, it wasinitially determined that the loading concentration for control(untreated) samples within the Bauer-McNeft classifier shows similarefficiencies at 10 oven dried gram and 20 oven dried gram loadings. Asset forth in Table 1 and graphically represented in FIG. 2, the ashseparation efficiency of control (untreated) sludge samples remainconstant at the 10 and 20 gram loadings. Therein after, 20 gram loadingruns were used to increase the amount of material collected and used inthe remaining test. The data as depicted in FIG. 2 confirms experiencewithin the industry that it is difficult to recover useful fibers fromwaste sludge since the recovered product has a high ash content whichlimits the use of the fibers.

[0081] As set forth in FIG. 4, the ash content associated with recoveredfibers from treated sludge is significantly reduced for both the 2minute and 5 minute treatment intervals. This finding is furthersupported by the data set forth in FIG. 3 that indicates the combinedweight of the 200 mesh and larger control group of recovered fibers fromuntreated sludge is higher than the weight of treated sludge recoveredfibers. The combined data indicates that the untreated recovered fiberweight is greater as a result of the increased levels of ash particles.Stated another way, the steam treatment allows a fiber recovered productwhich has a significantly lower ash content than is otherwise obtained.

EXAMPLE 1

[0082] Canadian Standard Freeness Measurements

[0083] The prepared handsheets were subjected to several tests, namelyCanadian Standard Freeness values, burst index, tensile index, tensilestretch, tear index, and opacity.

[0084] As best seen in reference to Table 2 and FIG. 5, handsheetsprepared from the fibers recovered following steam explosion of thesludge compare favorably at 30 percent, 70 percent and 100 percentloading levels to the control sheet of zero percent treated fibers withrespect to the Canadian Standard Freeness values. Canadian StandardFreeness values were determined according to protocols established inTAPPI Test Methods T-227 OM-94.

[0085] Compared to untreated fibers, the treated 100 percent recoveredfiber improved the freeness values from a value of 300 to between 470 to490. It is believed that the improvement are the results of a decreasein the fine and ash content in the reclaimed fibers along with steamexplosion induced changes in fiber morphology.

EXAMPLE 2

[0086] Burst Index of Handsheets

[0087] The burst index of the handsheets were determined in accordancewith established protocols in TAPPI Test Method T 403 “Bursting Strengthof Paper” and as further referenced in TAPPI 220-sp-96 procedure forPhysical Testing of Pulp Handsheets.

[0088] As seen in Table 2 and in FIG. 6, the burst index of thehandsheet using reclaimed fibers from treated sludge consistentlyexceeds the burst index of untreated sludge fibers.

EXAMPLE 3

[0089] Tensile Index Values of Handsheets

[0090] Tensile index of samples was calculated by dividing the sampletensile strength by the sample basis weight. Tensile strength refers tothe maximum load or force (i.e., peak load) encountered while elongatingthe sample to break. The tensile strength was determined with an InstronModel 1122 Universal Test Instrument in accordance with Test MethodTAPPI T 404 cm-82. Each sample was about 2.54 centimeters wide and theinitial separation between the tester jaws prior to elongation was about12.7 centimeters.

[0091] The tensile index properties of sheets having reclaimed fibers,as seen in FIG. 7, exceeds the values of the untreated sludge fibers.

EXAMPLE 4

[0092] Tensile Stretch Values of Handsheets

[0093] The tensile stretch values are determined as a percentage of thetensile index values as set forth above in Example 3. As seen inreference to Table 2 and in FIG. 8, the tensile strength values oftreated recovered fibers is improved compared to the untreated recoveredfibers.

EXAMPLE 5

[0094] Tear Index of Handsheets

[0095] The tear index was calculated by dividing the tearing load by thesample basis weight. The tearing load measures the toughness of amaterial by measuring the work required to propagate a tear when part ofa specimen is held in a clamp and an adjacent part is moved by the forceof a pendulum freely falling in an arc.

[0096] The following method was used to determine the tearing load ofthe handsheets. This method determined the average force required topropagate a tear starting from a cut slit in the material being tested.The higher the number, the greater the force to tear the specimen.

[0097] This procedure is specific to a falling-pendulum (Elmendorf-type)instrument. Desirably, the tester is equipped with a pendulum that has adeep cutout (recessed area) on the pendulum sector andpneumatically-activated clamps. The tester used was sold under the tradedesignation Lorentzen and Wettre brand, Model 09ED. This tester may beobtained from Lorentzen Wettre Canada Inc., Fairfield, N.J. 07004.

[0098] In addition to the tester, a specimen cutter was used capable ofproviding 63.0±0.15 mm (2.5±0.006 in.) specimens. It is recommended thatthe specimens be cut no closer than 15 mm from the edge of the materialand the specimens be taken only in areas that are free from folds,creases, and crimp lines. The handsheet specimens were cut to 63±0.15 mmby 73±1 mm and placed facing up in the same direction. Additionalequipment included a 50 g weight.

[0099] Specimens were conditioned at laboratory conditions for 24 hoursprior to testing. The tests were conducted in a standard laboratoryatmosphere of 23±1° C. (73.4±1.8° F.) and 50±2% relative humidity.

[0100] The number of plies needed for the test results to fall between20 to 60 on the linear range scale of the tear tester was determined.The 63 mm length of the handsheet specimens was run vertically on thetear tester.

[0101] The tester was placed a level surface free from noticeablevibrations and leveled. Afterwards, testing of a specimen was begun byverifying that the power was on. Next, the rotary dial was set to thenumber of plies to be torn. That being done, the number button waspushed and the cutting lever was pushed down. Afterwards, the digitalreadout was verified as correct. Next, the specimen was placed betweenthe clamps with the edge of the specimen aligned with the front edge ofthe clamp. If more than one sheet was tested, the sheets were placedfacing in the same direction. That being done, the clamp button waspushed to close the clamps. Afterwards, a slit was cut in the specimenby pushing down on the cutting knife lever until it reaches its stop.The slit was clean with no tears or nicks. Next, the pend button waspushed to release the pendulum. That being done, the pendulum was caughton the back swing and positioned to the starting position after thependulum traveled one full swing. Afterwards, the pend button wasdepressed to raise the stop once the pendulum was behind it. The valuewas recorded unless the tear line deviated more than 10 millimeters. Ifthe deviation was more than 10 millimeters, the specimen was discardedand a new specimen tested.

[0102] The results were recorded in grams centimeter. The values werereported to the nearest whole number. The following conversion factorswere used with units which had a 1600-gram capacity and did notautomatically convert the test result: # of sheets Multiply by # ofsheets Multiply by 1 sheet 16  8 sheets 2 2 sheets 8 10 sheets 1.6 4sheets 4 12 sheets 1.33 5 sheets 3.2 16 sheets 1

[0103] As seen in reference to Table 2 and in FIG. 9, improvements areseen in the tear index values of the recovered fibers.

EXAMPLE 6

[0104] Opacity Determinations

[0105] The opacity coefficient was determined in accordance withestablished protocols in TAPPI test method T 220 sp-96 and is set forthin Table 2 and illustrated graphically in FIG. 10.

[0106] As recorded in Table 2, additional measurements of specificvolume, tensile energy absorption, scattering coefficient and porositydeterminations were evaluated and recorded. The evaluations conform toTAPPI standards. The specific volume was determined by measuring thethickness of the paper and dividing by the measured papers' basisweight. The thickness of the paper was determined in accordance withTAPPI standard T 411 om-89. The procedure deviated from the TAPPIstandard by measuring the thickness of five specimens rather than theten TAPPI specimens in conducting three measurements rather than fiveTAPPI measurements.

[0107] In reference to Table 2 and to FIG. 10, handsheets incorporatingrecovered treated fibers have a lower opacity than handsheets withuntreated recovered fibers. Again, the lower opacity of the treatedrecovered fibers is attributed to a lower ash content of the sourcefibers.

[0108] While not wishing to be limited by theory, it is believed thatthe above noted improvements to fiber separation and fiber quality areindicative of several changes brought about by the steam explosiontreatment. One, it is seen that the treatment of the waste sludge has abeneficial effect on the separation dynamics of the particulate ash. Thesteam treatment may render a smaller ash particle size, making thefiber/ash separation easier.

[0109] A second noted benefit of the steam explosion treatment processis that the quality of the recovered population of fibers has improvedfiber characteristics as evaluated in the handsheet properties. It isbelieved that the steam treatment process alters the fiber morphology byincreasing the curl index as well as increasing the fiber diameter. Asnoted in the co-inventor's application referred to and incorporated byreference above, the steam explosion of isolated cellulosic fibersimproves the fibers liquid absorption and liquid handling properties.

[0110] Both the increase in curl index and the change in morphologyprovide similar separation efficiency in fines. While the finepopulation, as determined by the fiber/fine residue which passed through#200 and larger mesh screen, was not separately evaluated, the fines arebelieved to undergo similar changes. As noted above, the separationefficiency of the fines from ash is increased. As such, a recoveredpopulation of fines may be separated from the waste, reducing the solidcontent of the waste stream. Further, it is believed that the cellulosicfines, following steam treatment, also have improved fiber qualitiescompared to untreated fines. As such, the treated fines can beincorporated into certain paper products.

[0111] To the extent the steam explosion treatment alters the cellulosicfibers' morphology, it should be noted that the population of recoveredfibers likely contained material which, untreated, would have beenclassified as a fine. In other words, the curling and diameter changesseen in steam-treated fibers likely produced altered fines having anincreased curl index and/or larger diameter. Either event increases thenumber of fines which would be captured in the Bauer McNett classifieralong with the longer fiber population. As such, the data supports theconclusion that increased loadings of fines and fibers from steamtreated sludge can be added to paper products.

[0112] The above embodiments are directed towards a recovered fiberproduct from the waste sludge of a paper recycling facility. However,the scope of the present invention is not limited to any specific wastestream. Virgin chipping operations and paper making operations allgenerate a waste stream which contains significant levels of fibers andfines in the waste stream. The current invention provides a processwhich can increase the recovery of fibers and fines from the wastestream. Further, the steam explosion improves the recovered fiberscharacteristics useful in paper products.

[0113] Although desired embodiment of the invention has been describedusing specific terms, devices, and methods, such description is forillustrative purposes only. The words used are words of descriptionrather than of limitation. It is to be understood that changes andvariations may be made by those of ordinary skill in the art withoutdeparting from the spirit and scope of the present invention which isset forth in the following claims. In addition, it should be understoodthat aspects of the various embodiments may be interchanged, both inwhole or in part.

What is claimed is:
 1. A process of recovering fibers from waste paperrecycling sludge comprising: providing a waste sludge stream comprisinga plurality of fibers and fines; placing said waste sludge in a firstvessel; bringing an interior of said vessel and said waste sludge to anelevated temperature and pressure; maintaining said elevated temperatureand pressure for an effective time interval; discharging said wastesludge from said first vessel to a second vessel, said second vesselbeing sufficiently vented to maintain a pressure drop during saiddischarge step, and to thereby provide a treated sludge productcomprising treated fibers and fines; passing said treated sludge througha separator to separate and collect a portion of said treated fibers andsaid treated fines from said sludge.
 2. The process according to claim1, wherein said elevated temperature is within the range of about 130°C. to about 250° C.
 3. The process according to claim 1, wherein saideffective time interval is between about 0.5 minutes to about 30minutes.
 4. The process according to claim 1, wherein said elevatedpressure is about 100 to about 300 psi.
 5. A process of converting wastefibers from a fiber process waste stream to a recoverable fiber havingimproved fiber properties comprising: providing a waste streamcomprising a mixture of fibers and ash from a fiber processing facility;exposing said waste stream to an elevated temperature and pressure;releasing rapidly said pressure from said waste stream, therebyproviding a plurality of treated fibers within a treated waste stream;and separating said treated fibers from said waste stream.
 6. Theproduct according to the process of claim 5 wherein said mixture offibers further comprises a plurality of fines.
 7. The process accordingto claim 5 wherein said elevated temperature is within the range ofabout 130° C. to about 250° C.
 8. The process according to claim 5wherein said elevated pressure is about 100 to about 300 psi.
 9. Theprocess according to claim 5 wherein said waste stream is from a wastepaper recycling operation.
 10. The process according to claim 5 whereinsaid waste stream is from a paper making operation.
 11. A process ofconverting waste fibers from a fiber process waste stream of a papermaking facility to a recoverable fiber having improved fiber propertiescomprising: providing a waste stream from a papermaking facilitycomprising a mixture of a plurality of fibers and ash; exposing saidwaste stream to an elevated temperature and pressure; releasing rapidlysaid pressure from said waste stream, thereby providing a plurality oftreated fibers within a treated waste stream; and separating saidtreated fibers from said waste stream.
 12. A process of improving theuseful properties of fibers comprising: providing a first supply offibers, said fibers contained within a portion of a waste stream from apaper fiber processing operation; subjecting said fibers in said wastestream to an elevated temperature; discharging said fibers and saidwaste stream from a first pressure environment to a second pressureenvironment, said first pressure being greater than said secondpressure; separating a portion of said fibers from said waste stream,thereby providing a second supply of fibers, said second supply offibers having improved fiber qualities than untreated fibers.
 13. Theprocess according to claim 12 wherein said portion of a waste streamfurther comprises a first supply of fines.
 14. The process according toclaim 13 wherein said separating step further comprises separating asupply of treated fines from said treated waste stream.
 15. The processaccording to claim 14 wherein said supply of fines have improved fiberproperties for paper product usage than said first supply of fines. 16.The process according to claim 12 wherein said waste stream furthercomprises a waste stream from a paper recycling facility.
 17. Theprocess according to claim 11 wherein said separated treated fibers arereintroduced into a paper making process stream.
 18. The processaccording to claim 12 wherein said waste stream is from a waste paperrecycling operation.
 19. The process according to claim 12 wherein saidwaste stream is from a paper making operation.
 20. A modified cellulosicfiber that is prepared by a process comprising steam explosion of fiberscontained within a fiber processing waste stream, said steam explosionoccurring at a pressure at super-atmosphere and at a temperature rangeof about 130° C. to about 250° C. to give a modified cellulosic fiberhaving an altered morphology which increases the separation efficiencyof the modified fiber from the waste stream.
 21. The modified fiber ofclaim 20 wherein the modified fiber is in the form of a fine.
 22. Themodified fiber of claim 20 wherein said altered morphology includes acurl index greater than a curl index of fibers within said unmodifiedwaste stream.
 23. An absorbent structure comprising modified cellulosicfibers according to the process of claim
 20. 24. An absorbent structurecomprising treated fibers according to the process of claim 5.